from Central's ODATA docs :
The nonstandard $wkt querystring parameter may be set to true to request that geospatial data is returned as a Well-Known Text (WKT) string rather than a GeoJSON structure.
In that case, geojson_columns parameter in odk_central_to_pg(text, text, text, integer, text, text) should be droppped in a second signature of the function
from Central's ODATA docs :
In that case, geojson_columns parameter in odk_central_to_pg(text, text, text, integer, text, text) should be droppped in a second signature of the function